The present invention relates to a data processing apparatus, a data processing method, and a program.
Recently, recording media such as optical disks that are significantly enhanced in recording rate have come into general use. This has helped to realize long-time recording of video data with comparatively high picture quality.
Japanese Patent Laid-Open No. Hei 11-136631 discloses a method whereby pictures of the same content are prepared in two kinds, i.e., high-resolution and low-resolution video data, when recorded to an optical disk so that the video data with an optimum resolution may be selected depending on the purposes such as editing work.
Compared with audio data and text data, video data are huge in volume. That means the processing of video data is subject to significantly heavier loads than the processing of audio data or text data despite today's appreciable advances in the recording rate of recording media.
Video data processing apparatuses operated by users are so encumbered with the huge volume of video data that the result of video data processing is often slow to materialize. Such reduced operability of the apparatus is frustrating to the users. Illustratively, a user may operate a video data editing apparatus to start reproducing video data from a desired position on an optical disk. In that case, reproduction of video data from the desired position may take inordinately long time before getting started, which is annoying to the user.
One method for bypassing the problem above is to reduce the recording rate of video data to the optical disk. This method necessarily entails deterioration of picture quality during reproduction of video data. In particular, the method is unfit for business-use apparatuses because the apparatuses are required to record and reproduce video data at appreciably higher rates than their home-use counterparts.
In order to reduce the recording rate while decreasing picture quality deterioration, a method has been proposed by which video data are compressed by means of MPEG (Moving Picture Experts Group) encoding or the like. However, if video data are compressed illustratively by MPEG encoding, the decoding process often takes more time than is deemed acceptable. This can result in even less operability than before.
Specifically, common MPEG encoding involves encoding video data in a consecutive GOP (Group of Pictures) sequence. That means decoding a certain frame (field) sometimes requires decoding another GOP frame. In that case, it takes a long time to reproduce a desired frame after the user has performed the operation to reproduce that frame.
More specifically, to decode a B picture in a GOP of interest sometimes requires decoding a P picture in the preceding GOP. Furthermore, decoding that P picture in the preceding GOP may require decoding another P picture and an I picture in the same GOP. Overall, decoding the desired B picture in the GOP of interest may involve decoding many other pictures in advance. From the time that the user orders reproduction of the desired B picture in the GP of interest until the B picture is actually decoded and output, it may take an inordinately long time to decode the many other pictures.
Where a removable recording medium such as an optical disk is in use, it takes more time for the apparatus to find a desired picture on the disk than, say, on a hard disk drive. That is because a seek to a specific position on the optical disk takes longer than an access operation on the hard disk. The prolonged access time detracts from a “brisk” feel desired by the user in what is known as the cue-up operation on pictures.
Meanwhile, technology today has made nonlinear editing and nondestructive editing available. The nondestructive editing method involves setting what may be called edit points (known as in-points and out-points) with regard to material data, without editing (i.e., destroying) the material data themselves. More specifically, nondestructive editing involves preparing a list called a play list or an edit decision list made up of the edit points established during editing work on the material data of interest. The result of the editing is reproduced in accordance with the play list. That is, the material data are reproduced in keeping with the edit points described in the play list. Conventionally, where material data are to be encoded irreversibly in, say, MPEG format, the material data need to be first decoded. The decoded material data are then spliced as desired and encoded in MPEG format. By contrast, the nondestructive editing method has no need for such complicated processing involving decoding and encoding steps resulting in the deterioration of picture quality.
If a body of continuous material data ranging from one edit point (in-point) to the next edit point (out-point) derived from the above-described nondestructive editing is called a clip, then the result of nondestructive editing may be said to be reproduced on a clip by clip basis. Whereas consecutive material data are generally recorded on a physically continuous recording area on the optical disk, different clips constituting the material data are usually recorded in physically discrete recording areas on the same disk.
When the object to be reproduced shifts from, say, a first clip to a second clip on a disk apparatus reproducing the optical disk containing these clips, a track jump is effected starting from a recording area that has the first clip to another recording area that accommodates the second clip. In such a case, the track jump is followed by a rotational delay in which the beginning of the ensuing clip is being found. At the end of the rotational delay time, the next clip is reached and decoded for reproduction.
That is, the shift from one target clip to the next involves a track jump to the next clip followed by a rotational delay, a read and a decode operation, in that order, before the next clip is readied for output. At the end of the currently reproduced clip (called the current clip hereunder), it may be desired to start reproducing immediately the clip to be reproduced next (called the next clip). In that case, it is necessary to complete the preparations for outputting the next clip before reproduction of the current clip comes to an end.
It takes time to make the preparations for outputting a clip; they include a seek (made up of a track jump and a rotational delay) to the clip in question, a read, and a decode operation. Because the preparation time varies significantly depending on the performance of the disk apparatus in use, nondestructive editing allows for the differences in performance between optical disk reproducing apparatuses so that reproduction will not be interrupted upon shift from one target clip to another.
However, some removable recording media such as the optical disk are sometimes reproduced by a disk apparatus offering appreciably less performance than the disk apparatus that has effected nondestructive editing. In that case, seek and read operations on the data from the optical disk may take more time than is expected, which may leave the preparations for outputting the next clip incomplete at the end of the current clip being reproduced. As a result, the output (i.e., display) of the current clip may come to an end without being followed immediately by the output of the next clip, thereby interrupting the flow of clip reproduction.
The present invention has been made in view of the above circumstances and provides a data processing apparatus, a data processing method, and a program for improving the response of a disk reproducing apparatus in order to minimize the duration to obtain reproduction output following issuance of a reproduction order and to avert any disruption of continuous reproduction.